In an electronic device, an electronic component such as an IC chip or a power element, is mechanically joined to another component such as a wiring board or a lead frame, through a joining material. Furthermore, the mechanically joined components are sealed by using a mold resin
For example, solder such as Pb-free solder which does not contain Pb has been used, in recent years. The electronic component may be used in a high temperature equal to or higher than 200° C. However, Pb-free solder which can be used in such high temperature has not been found, at the present time.
Patent Document 1 (JP 2008-147469A) proposes an electronic device, in which an electronic component is mechanically joined to a member to be joined via a metal conductor made of a porous noble metal material as a joining material. The metal conductor is formed by sintering a mixture of Ag particles and an organic material. The sintered Ag material is formed into a porous shape.
The electronic device includes an electronic component such as an IC chip, a power element, etc., which has a large-scale integrated circuit. In recent years, because the power density rises in the electronic component, heat generation amount generated from the electronic component tends to increase, and thereby it is necessary to use a joining material having a high heat conductivity.
The inventors of the present applicant studied about the electronic device of Patent Document 1, in which the electronic component is mechanically joined to the member to be joined via the porous metal conductor. As an example, the Ag metal conductor has a high heat conductivity (for example, 420 W/mK), and is sintered to be used for the metal joining.
However, when the porous metal conductor is used for the metal joining, the mechanical strength of the metal joining is relatively low because the contact surfaces between the metal particles are small in the metal joining.
In order to increase the mechanical strength, the joining portion between the electronic component and the member to be joined may be sealed by using a mold resin.
In this case, the mold resin can be used to restrict a bending of the metal conductor generated due to the difference of coefficients of linear expansion between the components, thereby reinforcing the mechanical strength of the metal conductor.
However, the end surface of the metal conductor is also sealed by using the mold resin via a primer, because the end surface of the metal conductor is exposed between the electronic component and the member to be joined. The metal conductor made of noble metal, such as Ag, as described above, generally has hydrophobicity, and thereby the adhesiveness of the metal conductor with respect to the mold resin or the primer is relatively low.
Thus, even when the connection portion of the metal conductor is sealed by the mold resin, the mold resin and the primer may be easily separated from the metal conductor.